title: A network of interdependent molecular interactions describes a higher order Nrd1-Nab3 complex involved in yeast transcription termination.
abstract: Nab3 and Nrd1 are yeast heterogeneous nuclear ribonucleoprotein (hnRNP)-like proteins that heterodimerize and bind RNA. Genetic and biochemical evidence reveals that they are integral to the termination of transcription of short non-coding RNAs by RNA polymerase II. Here we define a Nab3 mutation (nab3Δ134) that removes an essential part of the protein's C terminus but nevertheless can rescue, in trans, the phenotype resulting from a mutation in the RNA recognition motif of Nab3. This low complexity region of Nab3 appears intrinsically unstructured and can form a hydrogel in vitro. These data support a model in which multiple Nrd1-Nab3 heterodimers polymerize onto substrate RNA to effect termination, allowing complementation of one mutant Nab3 molecule by another lacking a different function. The self-association property of Nab3 adds to the previously documented interactions between these hnRNP-like proteins, RNA polymerase II, and the nascent transcript, leading to a network of nucleoprotein interactions that define a higher order Nrd1-Nab3 complex. This was underscored from the synthetic phenotypes of yeast strains with pairwise combinations of Nrd1 and Nab3 mutations known to affect their distinct biochemical activities. The mutations included a Nab3 self-association defect, a Nab3-Nrd1 heterodimerization defect, a Nrd1-polymerase II binding defect, and an Nab3-RNA recognition motif mutation. Although no single mutation was lethal, cells with any two mutations were not viable for four such pairings, and a fifth displayed a synthetic growth defect. These data strengthen the idea that a multiplicity of interactions is needed to assemble a higher order Nrd1-Nab3 complex that coats specific nascent RNAs in preparation for termination.
authors.affiliation: Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322.
authors.forename: Travis J
authors.initials: TJ
authors.lastname: Loya
authors.affiliation: Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322.
authors.forename: Thomas W
authors.initials: TW
authors.lastname: O'Rourke
authors.affiliation: Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322.
authors.forename: Natalya
authors.initials: N
authors.lastname: Degtyareva
authors.affiliation: Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322. Electronic address: dreines@emory.edu.
authors.forename: Daniel
authors.initials: D
authors.lastname: Reines
mesh_terms: D020816:Amino Acid Motifs; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D055503:Protein Multimerization / Q000502:physiology; D012319:RNA Polymerase II / Q000235:genetics / Q000378:metabolism; D012331:RNA, Fungal / Q000096:biosynthesis* / Q000235:genetics; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D061806:Transcription Termination, Genetic / Q000502:physiology*
chemical_list: D046912:Multiprotein Complexes; C090564:NAB3 protein, S cerevisiae; C491211:NRD1 protein, S cerevisiae; D009687:Nuclear Proteins; D012331:RNA, Fungal; D016601:RNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; D012319:RNA Polymerase II
keywords: Gene Regulation; Nab3; Nrd1; Polyglutamine; RNA; RNA Polymerase II; RNA-binding Protein; Transcription Elongation Factors; Transcription Termination